The present invention relates to a saddle-riding type compact snow vehicle having substantially the same upper frame structure as a motorcycle and mounting a steering ski instead of a front wheel of the motorcycle and an endless track type driving device instead of a rear wheel of the motorcycle.
As is known in the prior art (e.g., U.S. Pat. No. 4,613,006), an endless track vehicle, such as a snow vehicle, is provided with a steering ski at a front portion of the vehicle body and with an endless track device having an endless track belt at a rear portion of the vehicle body. The endless track device is driven by an engine, and it includes a driving wheel and a guide roller both mounted on swing arms swingably supported to the rear portion of the vehicle body. The endless track belt is wrapped around the driving wheel and the guide roller.
In the above construction of the vehicle, the endless track device and the swing arms are swung about a pivotal portion relative to the vehicle body frame, causing fluctuation in the contact area of the endless track belt against a snow surface, or the like. When the vehicle is driven in deep snow, the snow is dug by the rotative driving of the endless track device, resulting in a phenomenon such that the vehicle body of the snow vehicle, except the endless track device, comes into contact with the snow surface, and the endless track device is caused to idly operate in the snow (such a phenomenon will hereinafter be referred to as "stack"). Accordingly, it is necessary to prevent the stack as mentioned above.
Further, an amount of lateral projection of the rear fork and the rear arms in the prior art snow vehicle is large, causing interference with standing trees, or the like, during travelling and interference with the snow surface upon turning of the vehicle. Accordingly, it is desired to avoid such interferences, thereby improving the ability of the vehicle to move upon passing through narrow areas and reducing its running resistance due to the snow. Furthermore, it is also necessary to smoothly steer the steering ski, so as to improve the running performance. Other compact saddle-type riding snow vehicles are also known in the prior art. For example, Japanese Patent Laid-Open Publication No. 58-39581 discloses an off-road running vehicle mounting a sled instead of a front wheel of a motorcycle and an endless track type travelling device instead of a rear wheel of the motorcycle. This vehicle is suitable for running on sandy or marshy land, and especially on a snow surface. The endless track type travelling device of this reference includes a wheel supporting frame, a driving wheel supported to a front portion of the frame, and a driven wheel supported to a rear portion of the frame. The wheel supporting frame is supported through rod members to an upper body frame provided at a rear portion of the vehicle body. The wheel supporting frame is formed at its front end with forwardly upwardly inclined arms which are pivotally supported to pivotal portions of swing arms of the motorcycle. The driving wheel is driven by an engine through chains. An endless track is wrapped between the driving wheel and the driven wheel. The endless track is comprised of an endless rubber belt with a toothed belt fixedly attached to an inner circumferential surface of the endless rubber belt and adapted to engage sprockets of the driving wheel and the driven wheel, and a plurality of metal lugs provided on an outer circumferential surface of the endless rubber belt and arranged at circumferentially equal intervals.
Another conventional snow vehicle is disclosed in Japanese Utility Model Publication No. 49-10603, for example. This snow vehicle includes a rear wheel of a motorcycle, a tension roller provided behind the rear wheel, and a flexible endless travelling belt wrapped between the rear wheel and the tension roller in such a manner as to define a triangular space therewithin. The flexible endless travelling belt provides a contact surface adapted to flatly contact the snow surface.
In turning a normal motorcycle, the vehicle body thereof is inclined to the side of the turning to thereby provide smooth turning motion; however, in turning the snow vehicle, as mentioned above, it is hard to incline the vehicle body of the snow vehicle since the contact surface of the endless belt contacting the snow surface is flat, and the width of the endless belt is normally large so as to reduce the contact pressure against the snow surface. If the vehicle body of the snow vehicle is inclined upon turning, an outer-diameter side portion of the contact surface is separated from the snow surface, and only an inner-diameter side portion of the contact surface contacts the snow surface. As a result, the contact pressure is increased, and the driving or propelling force is reduced. Further, as the endless belt having a large width is inclined, the center of gravity of the vehicle body is vertically varied, thereby reducing the riding comfort of the driver.
To solve this problem, there has been proposed in Japanese Patent Laid-Open Publication Nos. 59-18083 and 58-136581 a snow vehicle having a rocking mechanism for transversely rocking the vehicle body relative to an endless track or belt. However, this rocking mechanism is complex and the turning performance of vehicles employing it is not satisfactory since the entire width of the endless track remains in contact with the snow surface.
Also addressed is the problem of providing a cover for an endless track belt so as to prevent snow, or the like, from being caught up by the endless track belt during its operation and scattered against the rider and vehicle components. In a device with articulation between elements of the apparatus that are covered such that the swing arms and the rear arms are arranged to swing with respect to each other, it is necessary to define a large space between the track belt and the track belt cover, if the track belt cover is mounted to the swing arms in a conventional manner. Consequently, the scattering of snow, or the like, caught up by the track belt cannot be adequately prevented.
It is accordingly an object of the present invention to provide a snow vehicle having improved running performance.
It is another object of the present invention to provide a saddle-riding type compact snow vehicle, wherein the endless track can readily follow the inclination of the vehicle body, and a contact area of the endless track contacting the snow surface can be increased to prevent an increase in contact pressure and a decrease in driving force upon turning of the vehicle.
According to still another object of the present invention, a track belt cover is provided in such a vehicle which can effectively prevent the scattering of the snow, or the like.